The present invention is directed to the testing of electronic circuit boards and in particular to the fixtures used for in-circuit testing.
It is desirable to subject many types of complex circuit boards to in-circuit testing, i.e., to the introduction and sensing of signals at "interior" nodes, which are not brought out to the board's edge connector. Such in-circuit testing requires probing of a large number of test points on the board, each of which must be driven or sensed by test instruments. Fortunately, the number of instruments that a tester needs to employ for in-circuit testing is typically much lower than the number of test points; since only a single device or group thereof is typically tested at one time, only a relatively small subset of the test points needs to be driven and/or sensed simultaneously. Consequently, connections of the instruments to probes by which signals are coupled between the instruments and test points can be made by way of switch circuitry, often referred to in the art as "scanners," that enables a given instrument to be coupled to different test points at different times during a given board's in-circuit test.
The use of such multiplexing thus limits the required amount of tester resources, but resource requirements are nonetheless high on testers capable of performing sufficiently comprehensive in-circuit tests of some of the most-complex circuit boards.